1. Field of the Invention
This invention relates to surgical instruments, and is more particularly concerned with snare instruments used for removal of protruding tissue, such as tonsils, polyps and the like.
2. Description of the Prior Art
Conventional snares operate so as to pull a wire loop, attached to a center rod, back into a sheath. For this purpose, the rod is provided with a pair of finger rings which are attached to the rod and a thumb ring which is attached to the tube. This structure has the advantage of providing the normal leverage of hand closure so that sufficient strength is available to accomplish removal of the tissue.
The disadvantage of conventional snares resides in the coupling between the finger rings and the rod. In one design the finger rings are attached to the rod through an elongate slot in the tube which permits extension of the distal end of the rod for threading of the wire loop and a travel upon closure of the hand which is sufficient to pull the rod sufficiently into the tube so that the loop is collapsed. In this context, it should be understood that the term "collapse" refers to decreasing the size of the loop an amount which is sufficient to cause separation of the tissue from the body.
In another conventional design, the tube is provided at the proximal end with a slide which is offset from the axis of the tube. The thumb loop is carried at the proximal end of the slide and the finger loops are slidably mounted on the slide with one loop attached to the proximal end of the rod.
When conventional snares, such as those discussed above, are also adapted for electro-surgery, additional structural elements must be provided to electrically connect the rod to an electro-surgical power supply, while at the same time electrically isolate the rod and power supply from the operating personnel.
Another disadvantage associated with conventional snares involves the attachment of the wire loop to the distal end of the rod. Conventionally, the distal end of the rod is provided with two transverse holes for receiving respective ends of the wires, the ends then being folded forward so that during movement of the rod into the tube the ends do not snag, reverse direction and disconnect from the rod. It is readily apparent that the distal end of the rod must be accessible to operating personnel for the purpose of threading. This is conventionally done in two ways: (1) additional forward travel of the rod is provided for exposure of the distal end; and (2) the rod is removed from the tube, threaded and reinserted, which may also involve disconnection of the finger loops and/or disassembly of the instrument.